Blood Storm

Infectious Rage. Blood Storm's rage burns so hot and so bright that anyone or sentient thing near her becomes infected with berserker rage. When she enters into an Infectious Rage, creatures within 120 feet that can see or hear her, must succeed on a Wisdom saving throw (DC 19) or be infected.

The Infected gain all the benefits and disadvantages of the Barbarian Class feature Reckless Attack. They throw aside all concern for defense to attack the nearest creature with fierce desperation. Doing so gives them advantage on melee weapon attack rolls using Strength during their turn, but attack rolls against them have advantage.

This aura is centered on the Infector and moves with them and lasts until either the infected or infector dies, falls unconscious, moves outside of the 30foot radius or the infector ends their rage. The aura can be activated as many times as your Constitution modifier and resets at dawn. 

Regeneration.  Blood Storm regains 60 hit points at the start of her turn.

Extra Arms.  Blood Storm has two additional arms.

Magic Resistance. Blood Storm has advantage on saving throws against spells and other magical effects.

Blood Magic. All water-based magic that Blood Storm uses can also be done with the spilled blood of her enemies. 

Innate Spellcasting. Blood Storm's spellcasting ability is Charisma (spell save DC 21). The pit fiend can innately cast the following spells, requiring no material components:

At will: shape water, create or destroy water

3/day each:watery sphere, wall of water, Control Water

Legendary Resistance (5/Day). If Blood Storm fails a saving throw, she can choose to succeed instead. Limited Magic Immunity unless she wishes to be affected (she never does), Blood Storm is immune to spells of 5th level or lower. She has advantage on saving throws against all other spells and magical effects.

Spell Resisted. Blue Revenge will intercede and add its strength to Blood Storm's will. It will coo the caster "Better luck next time, deary." or something as equally condescending.

Melee effect Resisted. Blood Storm physiology is shifting constantly in a way that benefits her. The attack hit a patch of dragon scales that seem to come out of nowhere.

Art found on Pinterest.

Multiattack. The Blood Storm makes eight (two for each arm) attacks with its weapon: Blue Revenge.

Weapons. Blue Revenge Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 24 (2d12 + 8) slashing damage plus 21 (6d6) necrotic damage.

Sentient Blade with the following stats: Int. 18, Wis. 16, and Cha. 18. It has awareness out to 120 feet with hearing and dark vision. It speaks telepathically using a calm, inviting and delicate voice. It becomes whatever weapon the welder desires, even splitting itself into several fragments to accommodate dual welding. It is a jealous and protective weapon. It will not tolerate the abuse of the welder. It feeds on the blood of those cut by it to empower its welder further. 

Terrifying Laughter. Blood Storm relishes combat in a way that only a few can understand. As a reaction she let out a maniacal laugh to that cuts to the very core beings of any plane. If they are not under effect of Infectious Rage each creature of within 240 feet of Blood Storm and aware of her must succeed on a DC 20 Wisdom saving throw or become frightened for 1 minute.

Blood Storm can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Blood Storm regains spent legendary actions at the start of her turn.

Vampiric Blades (Costs 1 Action). The very nature of Blue Revenge is to feed. After Blood Storm has hit a target and as a reaction, her blade can cast vampiric touch at 9th level (9d6 necrotic dmg).   

Lightning Jump (Costs 1 Action). Teleportation. As a bonus action on her turn, Blood Storm can teleport anywhere that lightning is striking within her line of sight.